Microscopy Primer
Light and Color
Microscope Basics
Special Techniques
Digital Imaging
Confocal Microscopy
Live-Cell Imaging
Photomicrography
Microscopy Museum
Virtual Microscopy
Fluorescence
Web Resources
License Info
Image Use
Custom Photos
Partners
Site Info
Contact Us
Publications
Home

The Galleries:

Photo Gallery
Silicon Zoo
Pharmaceuticals
Chip Shots
Phytochemicals
DNA Gallery
Microscapes
Vitamins
Amino Acids
Birthstones
Religion Collection
Pesticides
BeerShots
Cocktail Collection
Screen Savers
Win Wallpaper
Mac Wallpaper
Movie Gallery

Interactive Tutorials

Particle and Wave Diffraction

One point of view envisions light as wave-like in nature, producing energy that traverses through space in a manner similar to the ripples spreading across the surface of a still pond after being disturbed by a dropped rock. The opposing view holds that light is composed of a steady stream of particles, much like tiny droplets of water sprayed from a garden hose nozzle. This interactive tutorial explores how particles and waves behave when diffracted by an opaque surface.

The tutorial initializes with particles of monochromatic red light (photons) impacting the surface of a opaque light stop with an incident angle of approximately 90 degrees. Upon encountering the stop, particles are either deflected (not illustrated) or pass by the object undeviated. The Particle/Wave slider, located beneath the light stop, can be utilized to morph the beam of particles into a planar wavefront. Prior to becoming a wave, the particles align themselves in waves. Light waves interact with the light stop by diffracting (or bending) into the shadowed region behind the opaque barrier. The mouse cursor can be employed to drag the opaque light stop back and forth in front of the oncoming waves or particles.

Particles and waves should behave differently when they encounter the edge of an object and form a shadow (Figure 1). Newton was quick to point out in his 1704 book Opticks, that "Light is never known to follow crooked passages nor to bend into the shadow". This concept is consistent with the particle theory, which proposes that light particles must always travel in straight lines. If the particles encounter the edge of a barrier, then they will cast a shadow because the particles not blocked by the barrier continue on in a straight line and cannot spread out behind the edge. On a macroscopic scale, this observation is almost correct, but it does not agree with the results obtained from light diffraction experiments on a much smaller scale.

When light is passed through a narrow slit, the beam spreads and becomes wider than expected. This fundamentally important observation lends a significant amount of credibility to the wave theory of light. Like waves in water, light waves encountering the edge of an object appear to bend around the edge and into its geometric shadow, which is a region that is not directly illuminated by the light beam. This behavior is analogous to water waves that wrap around the end of a raft, instead of reflecting away.

Contributing Authors

Robert T. Sutter, Matthew J. Parry-Hill and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.


BACK TO LIGHT: PARTICLE OR A WAVE?

BACK TO LIGHT AND COLOR

Questions or comments? Send us an email.
© 1998-2022 by Michael W. Davidson and The Florida State University. All Rights Reserved. No images, graphics, scripts, or applets may be reproduced or used in any manner without permission from the copyright holders. Use of this website means you agree to all of the Legal Terms and Conditions set forth by the owners.
This website is maintained by our
Graphics & Web Programming Team
in collaboration with Optical Microscopy at the
National High Magnetic Field Laboratory.
Last modification: Friday, Nov 13, 2015 at 02:19 PM
Access Count Since August 9, 2002: 84440
For more information on microscope manufacturers,
use the buttons below to navigate to their websites: